Methods, systems, and apparatuses for accurate measurement and real-time feedback of solar  ultraviolet exposure

ABSTRACT

System and methods for accurate measurement and real-time feedback of solar ultraviolet exposure for management of ultraviolet dose. The systems can include a wearable device and a mobile device, the system performing accurate measurement of UV exposure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the following three U.S.Provisional applications, which are incorporated by reference herein:62/209,813, filed Aug. 25, 2015; 62/233,173, filed Sep. 25, 2015; and62/233,190, filed Sep. 25, 2015.

This application incorporates by reference herein the disclosure of U.S.Publication No. 2015/0102208, filed Oct. 1, 2014.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

BACKGROUND

Ultraviolet (“UV”) light is radiation in the wavelength range of 260-400nm. It is part of the solar radiation that reaches the Earth, and hascritical impact on humans. The skin synthesizes Vitamin D on exposure toUV which makes UV necessary for health. But overexposure to UV can causeadverse effects such as sunburn, systemic reactions in autoimmunediseases such as lupus, or pharmaceutical phototoxicity in the shortterm, and non-melanoma and melanoma skin cancer, skin aging,pharmaceutical photoallergy, photogenotoxicity, and photocarcinogenicityin the longer term (‘adverse effects’ thereafter). Sensitivity to UVvaries from person to person, e.g., darker skin types scatter more UV inthe top layers of skin and hence are at lower risk for sunburn. However,their skin synthesizes less Vitamin D than lighter skins. Sun-relatedactivity also varies from individual to individual. Outdoor runners aremore exposed to UV than indoor treadmill runners. Certain professions,such as construction, involve large exposure to UV on a daily basis,while office jobs involve lower UV exposure. Under such circumstances,the primary way to be able to control any adverse event of overexposureis to have an accurate knowledge of personal UV dose. This is what isachieved by the proposed exemplary systems and methods, where thewearable device measures UV exposure and aggregates it to compute the UVdose, while the mobile device displays metrics and alerts to the userbased on this information. In alternative designs, the mobile device,which may be referred to herein as a “remote device,” can process one ormore signals and aggregate the information.

How to Measure Solar UV Radiation in a Way Relevant to Human Health?

In 1987, the human sensitivity to ultraviolet radiation was defined byDiffey and later adopted by the World Metereological Organization andthe World Health Organization (McKinlay, A. & Diffey, B. “A referenceaction spectrum for ultra-violet induced erythema in human skin”. CIE J17-22 (1987)). This sensitivity is called the erythema action spectrumand gives exponentially more importance to high-energy photons. Whenmeasured on a horizontal surface, this standard metric is called theultraviolet index (UV Index, or UVI).

What impacts human health is the integration of UV exposure over time,referred to herein as the “UV dose.” When the UV exposure is weightedaccording to the erythema action spectrum, the accumulated dose iscalled the “erythemal dose.”

Some UV measuring systems include a UV measuring diode, which convertsthe incident ultraviolet radiation signal to electric current, coupledwith additional circuitry. This can include an analog-to-digitalconverter (ADC), op-amp and microcontroller, such as is described inAmini N., Matthews E. J., Vandatpour A., Dabiri F., Noshadi H.,Sarrafzadeh M., “A Wireless Embedded Device for Personalized UltravioletMonitoring,” International Conference on Biomedical Electronics andDevices, pp. 200-205 (2009). Some examples of these systems are theSolarmeter® 6.5 UVI and the Genicom UV Index Meter. While such systemsmight be capable of approximately measuring UV, they are not accurate ina wide variety of situations, as has been reported in Corrêa, M. D. P.et al. “Comparison between UV index measurements performed byresearch-grade and consumer-products instruments.” Photochem. Photobiol.Sci. 9, 459-463 (2010), and Larason, T. C. & Cromer, C. L. “Sources oferror in UV radiation measurements”. J. Res. Natl. Inst. Stand. Technol.106, 649-656 (2001).

Why is Accuracy Important in UV Measurements?

Several diseases or pharmaceutical treatments are negatively orpositively (up to a certain point) impacted by UV exposure. Forinstance, UV exposure is sometimes used in the treatment of psoriasisand the dose of UV exposure used in these treatments is well defined. Onthe other hand, going over a threshold of UV dose can trigger symptomsin lupus patients, phototoxicity for certain drugs, or erythema andsunburn of the skin. Some clinical experiments have found the thresholdfor erythema (Sayre, R. & Desrochers, D. “Skin type, minimal erythemadose (MED), and sunlight acclimatization”. Am. Acad. dermatology 439-443(1981); Heckman, C. J. et al. “Minimal Erythema Dose (MED) testing”. J.Vis. Exp. e50175 (2013) doi:10.3791/50175) for instance but most UV dosethreshold are unknown—and they vary from person to person. Even when UVdose thresholds are known, it is important to know current dose relativeto such thresholds. Overestimation of UV dose can lead to less timeoutside, hindering the capacity of planning properly one's day.Underestimation can lead to longer periods spent while exposed to UV(whether it is in sunlight or in the shade), which can easily causeadverse effects. This makes accuracy of extreme importance in themeasurement of UV dose. Since UV dose is the UV exposure integrated overtime, it follows that accurately measuring UV dose implies alsoaccurately measuring the UV exposure.

An approximate forecast for the maximum daily UV Index is usuallyprovided by local weather services, but is largely inadequate formeasuring personal UV exposure. Whether a person is in the shade, indirect sunlight, in indirect sunlight, this forecast is the samealthough actual UV exposure varies dramatically.

What are the Advantages of Real-Time Measurement of UV Dose?

The importance of thresholds is already known—whether it is forUV-induced lupus symptoms, pharmaceutical phototoxicity, or erythema andsunburn. If the UV dose threshold is being approached, or has beenexceeded, this information needs to be conveyed to the user so thathe/she can act on it immediately. Otherwise it can lead to adverseeffects that might lead to hospitalization. It is for instance knownthat UV exposure has a systemic impact on lupus and evidence shows thatlupus patients experience more flares in the summer than in the winter,as reported in Chiche, L. et al. Seasonal variations of systemic lupuserythematosus flares in southern France. Eur. J. Intern. Med. 23,250-254 (2012).

The Importance of Separating UVB from UVA

The clinical literature, whether it is looking at skin cancer, VitaminD, photosensitivity, phototoxicity, photocarcinogenicity, differentiatesbetween UVB (280-320 nm wavelengths) and UVA (320-400 nm wavelengths).This is because the two types of UV have different impact on the humanphysiology. The depth of penetration of UV light into the skin increaseswith increasing wavelength. While UVB is absorbed in the upper layer ofthe skin, UVA is able to travel further into the skin. For this reason,UVA, although less energetic than UVB, has a significant impact onautoimmune reactions and phototoxicity/photosensitivity. Both UVB andUVA can cause redness of the skin, drug-induced reactions, and triggerthe immune system to react. Outside, under solar radiation, UVB raysburn the skin before UVA do. For these reasons, the medical communitystresses the importance of differentiating UVB and UVA when a UV dose isreported.

Previous methods have discussed chemical methods for measuringinstantaneous UV radiation, as well as accumulated UV dose, such as inU.S. Pat. No. 4,255,665 and U.S. Pat. No. 2,949,880. U.S. Pat. No.8,829,457 and U.S. Pat. No. 5,148,023 describe electrical devicesconnected to a display unit capable of monitoring UV dose. The lack of amobile device interface to interact with the device makes it lessaccurate since it cannot use information such as the location and localtime for correction. It also has no notion of real-time feedback to theuser. U.S. Pat. No. 9,068,887 is derived from “Amini,” but additionallyutilizes the knowledge of location (as obtained by the mobile device) tocorrect UV Index readings. Some drawbacks of the earlier references arethat they fail to utilize detection of operating environment, or sensororientation to correct UV Index readings. Other previous methods discussusing visible light to estimate UV exposure, such as U.S. Pat. No.9,360,364. That disclosure does not explain how they estimate UVexposure based on visible light, an arduous task since UV exposure doesnot correlate with visible light. A prime example of this lack ofcorrelation is overcast weather, where visible light and heat arereflected/scattered by the clouds, but UV is still largely transmitted.The disclosure in U.S. Pat. No. 9,360,364 would be inaccurate in suchsituations.

Real-Time Notifications

U.S. Pat. No. 6,426,503 and US20040149921 describe providing touch-basedfeedback (using vibration), or with an audible alarm, when safe exposurethresholds are reached. It does not use notification on the mobiledevice. U.S. Pat. No. 9,068,887 describes notifications on a mobiledevice, but requires the wearable to be constantly connected(wirelessly) to the mobile device.

Separation of UVA and UVB

US 20120241633 describes a method to measure UVA and UVB separately.This is a pure hardware method involving the use of a photodiode witheither a UVA filter or a UVB filter. The described hardware allows onlyone type of a measurement at a time.

User-Selectable Safe Thresholds

U.S. Pat. No. 9,068,887 describes “user-programmed safe thresholds”,which means users are able to select the safe amount of UV exposure thatthey are open to receiving. They use skin type information to select adefault threshold for each skin type. The medical literature shows,however, that every person has a unique threshold. An exemplary systemattempting to perform such measurements has previously been proposed inAmini. It includes a wearable device with sensors, which wirelesslycommunicates with a mobile device (such as a smartphone or tablet).

Improved methods, devices and systems are needed to overcomeshortcomings of the approaches described above.

SUMMARY OF THE DISCLOSURE

One aspect of the disclosure is a computer executable method for userselection of UV dose thresholds, comprising: presenting, on a display ofa remote device, a time history of a subject's UV dose; presenting, onthe display of the remote device, a time history of informationindicative of a subject's symptoms; presenting on the display auser-adjustable interface adapted to allow a user to select a UV dosethreshold based on the time history of information indicative of thesubject's symptoms.

In some embodiments the presenting steps present the time historiesbroken up into the same epochs of time, such as days, and optionallywhere the epochs of time are user-selectable.

In some embodiments the user-adjustable interface comprises at least oneof a text field, a slider, and a selectable menu.

In some embodiments the method further comprises presenting a user inputelement that allows for the recordation of a patient symptom, whereinthe symptom is recorded into the time history.

In some embodiments the selected UV dose threshold is input to a methodthat is adapted to indicate how much time the subject can remain incurrent conditions before reaching the UV threshold. The method can alsoinclude displaying on the remote device an amount of time before thesubject will reach the UV threshold.

In some embodiments the presenting steps occur simultaneously.

One aspect of the disclosure is a computer executable method forestimating an amount of time for a subject to remain in an environmentuntil they reach a limit of UV dose: receiving a current UV dose, a UVdose limit, and a current UV exposure, the current UV dose and currentUV exposure based on sensed UV light from a wearable UV light sensingdevice; using the current UV dose, the UV dose limit, and the current UVexposure to estimate an amount of time before a subject will reach theUV dose limit; and displaying the amount of time or an indicator of theamount of time on a display of either the wearable device or the remotedevice.

In some embodiments estimating an amount of time comprises estimating UVexposure using an estimated maximum UV exposure, local sunset time, andlocal sunrise time. The method can also include estimating maximum UVexposure using the current UV exposure, sunrise time, and sunset time.

In some embodiments the method further comprises communicating anupdated output indicative of an updated amount of time in response to anadditional current UV exposure based on sensed UV light from thewearable UV light sensing device.

In some embodiments the method further comprises estimating the currentUV exposure based on previous current UV exposures.

In some embodiments the method further comprises, in response to adetermination that the subject is indoors based on a signal receivedfrom a visible light sensor in the UV sensing device, displaying anindicator to the subject indicating that the UV exposure to the subjecthas been reduced.

The disclosure also includes devices (wearable or mobile) on which anyof the suitable computer executable methods herein can be stored. Forexample, a mobile device or a wearable device can include a storagedevice, the storage device storing any of the computer executablemethods herein.

One aspect of the disclosure is a wearable UV sensing device comprising:a wearable housing that comprises a UV sensor and a proximity sensor,the proximity sensor comprising a proximity light detector adapted todetect reflected light from a proximity light source.

In some embodiments the proximity light source is an infrared lightsource, and the proximity detector is an infrared detector.

In some embodiments the UV sensor is a UVI sensor. The wearable housingcan further include a UVA sensor.

In some embodiments the device also includes a visible light sensor. Theproximity sensor and the light sensor can be part of the same sensor.

In some embodiments the UV sensor is disposed in a central region ofhousing, in a top view of the device, such as in the middle of thehousing.

In some embodiments the proximity sensor is disposed closer to aperiphery of the housing than the UV sensor.

In some embodiments the proximity sensor comprises the light source andthe light detector. The light source can comprise an infra-red LED andthe light detector can comprise an infra-red detector.

In some embodiments the device includes an orientation sensor.

In some embodiments the device further includes an optical diffuserdisposed between a top housing layer and the UV sensor and proximitysensor.

The disclosure includes devices (wearable or mobile) on which any of thesuitable computer executable methods herein can be stored. For example,a wearable device can include a storage device, the storage devicestoring any of the computer executable methods herein.

One aspect of the disclosure is a wearable UV sensing device comprisinga UV sensor.

One aspect of the disclosure is a wearable UV sensing device comprisinga proximity sensor.

One aspect of the disclosure is a wearable UV sensing device comprisinga UVA sensor.

One aspect of the disclosure is a wearable UV sensing device comprisinga visible light sensor.

One aspect of the disclosure is a wearable UV sensing device comprisinga proximity sensor and a visible light sensor, and the proximity sensorand the light sensor can be part of the same sensor or they can bedifferent sensors.

One aspect of the disclosure is a computer executable method ofdetermining if a UV sensing device is at least partially covered,comprising: receiving information indicative of a signal from aproximity light detector that is disposed within a wearable UV sensingdevice, the information indicative of light reflected onto the proximitylight detector from a proximity light source disposed in the wearable UVsensing device; determining, based on the information received, if theproximity light source is covered by a material; and sending a signal toa remote device to initiate an alert to a user of the determination thatthe proximity light source is covered and that the material should beremoved from covering the proximity light source.

In some embodiments the determining step comprises characterizing anamount of light reflected onto the proximity light detector from theproximity light source. Characterizing an amount of light reflected ontothe proximity light detector can comprise comparing the amount of lightreceived with a proximity threshold.

One aspect of this disclosure is a computer executable method forautomatically entering sleep mode on a wearable UV sensor (optionallystored in a storage device of a wearable UV sensor), comprising:receiving information indicative of a signal from a visible light sensorthat is disposed in a wearable UV sensing device; using the informationto determine if a condition of darkness adjacent the UV sensor haspersisted for a period of time; and initiating a sleep mode for thewearable UV sensor if a determination has been made that a condition ofdarkness has persisted for a period of time.

In some embodiments using the information to determine if a condition ofdarkness adjacent the UV sensor has persisted for a period of timecomprises: comparing the information with a visible light threshold;incrementing a counter if the information is not above the visible lightthreshold; and comparing counts from the counter with a threshold count,wherein the initiating step comprises initiating a sleep mode if thecounts are greater than the threshold count.

In some embodiments the method further comprises maintaining an activemode of the UV sensing device if a determination has been made that acondition of darkness adjacent the UV sensor has not persisted for theperiod of time.

In some embodiments the method further comprises, after initiating sleepmode, initiating an active mode in which a UV sensor is activated basedon the information indicative of a signal from the visible light sensorif the information is greater than a visible light threshold.

In some embodiments the method further comprises receiving informationindicative of a signal from a proximity sensor in the UV sensing deviceand determining if a material covering the device is responsible for thecondition of darkness.

In some embodiments initiating a sleep mode comprises decreasing the useof the UV sensor.

In some embodiments initiating a sleep mode comprises maintaining a useof the visible light sensor.

One aspect of the disclosure is a computer executable method ofincreasing the accuracy of UV monitoring (optionally stored on a devicewith a storage device), comprising: receiving UVB information that isindicative of an intensity of UVB light sensed by a UV sensor, the UVsensor disposed in a UV monitor; comparing the UVB information with athreshold UVB level to make a first determination if the UV monitor isindoors or outside; receiving secondary information indicative of lightoutside of the UVB range sensed by the UV sensor or a second sensordisposed in the UV monitor; using the secondary information to make asecond determination about the environment of the UV monitor; using thesecond determination about the environment to select one of a pluralityof environment models for predicting the UV Index; and predicting the UVIndex with the selected model.

In some embodiments receiving secondary information comprises receivingsecondary information indicative of visible light sensed by a secondsensor, the second sensor being a visible light sensor disposed in theUV monitor, and wherein using the secondary information comprises usingthe secondary information to make a second determination about whetherthe UV monitor is outdoors and in the shade, or outdoors and in theopen. Making the second determination can comprise comparing thesecondary information indicative of visible light to a visible lightthreshold. The method can further include using the UVB information thatis indicative of an intensity of UVB light sensed by a UV sensor and thesecondary information indicative of visible light sensed by a secondsensor to make a further determination about whether the UV monitor isin an open cloudy environment, or in an open and sunny environment.Making the further determination can comprise calculating if apolynomial is above an open threshold, the polynomial comprising a firstvariable indicative of the UVB information, and a second variableindicative of the visible light sensed by the second sensor.

In some embodiments receiving secondary information comprises receivingsecondary information indicative of an intensity of UVA light, andwherein using the secondary information comprises using the secondaryinformation to make a second determination about whether the UV monitoris indoors and in direct sunlight, or indoors and not in directsunlight. Using the secondary information to make a second determinationcan comprise comparing the secondary information indicative of anintensity of UVA light to a UVA light threshold.

In some embodiments the computer executable method is stored in the UVmonitor.

In some embodiments the computer executable method is stored in a remotedevice, the UV monitor and the remote device adapted to communicate.

In some embodiments the method further comprises presenting informationon a remote device to the user, the information indicative of thepredicted UV index.

In some embodiments receiving UVB information that is indicative of anintensity of UVB light sensed by a UV sensor can comprise receiving UVBinformation that is indicative of an intensity of UVB light sensed by aUVI sensor.

One aspect of this disclosure is a computer executable method ofestimating UVA and UVB with a UVI sensor (optionally stored on a devicewith a storage device), comprising: receiving as input, from a remotedevice, a solar zenith angle; calculating a ratio comprising UVB and UVAusing the solar zenith angle; receiving as input UVI information that isindicative of an output signal of a UVI sensor; calculating an estimatedUVB using the UVI information and the calculated ratio comprising UVBand UVA; and calculating an estimated UVA using the UVI information andthe calculated ratio comprising UVB and UVA.

In some embodiments the ratio is a function of the solar zenith angle.

In some embodiments the estimated UVB is used in calculating a timehistory of UVB exposure of a subject, further comprising presenting thetime history of UVB on a display of the remote device.

One aspect of the disclosure is a computer executable method ofmodifying sensed UV signals based on orientation of a UV sensing device(which can be stored on a device with a storage device), comprising:receiving as input UV information indicative of UV light sensed by a UVsensor disposed in a UV sensing device; and estimating a UV irradianceincident normal to a face of a subject using an angle of tilt of the UVsensing device relative to a transverse plane of a subject, and the UVinformation, the angle of tilt derived from orientation sensorinformation from an orientation sensor disposed in the UV sensingdevice.

In some embodiments the UV information is indicative of UV light sensedby a UVI sensor.

In some embodiments the estimated UV irradiance is used in calculating atime history of UV exposure of a subject.

One aspect of the disclosure is a charging system for a wearable UVsensing device comprising: a wearable housing comprising a UV sensor, acentral conductor, and at least one annular conductor extending aroundthe central conductor, the central conductor and the at least oneannular conductor at a bottom surface of the housing; a chargerincluding at least first and second conductive contacts, wherein thefirst and second contacts are spaced from each other and the centralconductor and annular conductor are spaced from each other such that thefirst and second contacts are aligned with the central conductor and theannular conductor, respectively, when the housing and charger interface.

In some embodiments the charger further comprises a first magneticelement that is magnetically attracted to a second magnetic elementdisposed within the wearable housing. The first and second magneticelements can be positioned and configured such that their magneticattraction facilitates the alignment of the first and second contactswith the central and annular conductors, respectively. The first andsecond magnetic elements can be substantially the same size.

In some embodiments the central conductor is, in a top view, alignedwith the UV sensor.

One aspect of the disclosure is a wearable UV sensing system,comprising: a housing comprising a UV sensor and a first magneticelement; and a second magnetic element outside of the housing andadapted to have a magnetic attraction with the first magnetic element.

In some embodiments the second magnetic element is not physicallyattached to the housing.

In some embodiments the second magnetic element is physically attachedto the housing.

In some embodiments the first and second magnetic elements havesubstantially the same shape. The first and second magnetic elements canhave at least one dimension that is not the same.

In some embodiments the first magnetic element lies in a plane that isparallel with a bottom surface of the housing.

In some embodiments the first magnetic element is closer to the bottomsurface than a top surface of the housing.

In some embodiments the UV sensor is closer to a top surface of thehousing than the first magnetic element.

In some embodiments the first magnetic element, in a top view of thedevice, surrounds the UV sensor.

In some embodiments the first and second magnetic elements have annularconfigurations.

In some embodiments one of the first and second magnetic elements is amagnet and the other is a ferromagnetic material.

Some embodiments herein include systems, some of which include awearable device and a mobile device (which may be referred to hereinmore generally as a “remote” device), which perform accurate measurementof UVA and UVB. In some embodiments the systems perform accuratemeasurement of UVA and UVB exposure on the human face, which is theregion of the body the most exposed to UV. In some embodiments thewearable device comprises a unique combination of visible, UVA, UV Indexand proximity sensors. The sensors can be covered by a diffuser withcosine response. In some embodiments a magnetic attachment system isadapted and configured to be attached to the front of a user's clothing.The disclosure includes algorithms, or computer executable methods, forestimating UVA and UVB from the data collected from these sensors, whichcan be corrected using knowledge of the environment around the user(e.g., shade or indoors), and/or the orientation of the device. Thewearable device can also be made power efficient by using the visiblelight sensor to turn off operations at night. Some embodiments alsoinclude a real-time notification system, whereby the wearable is adaptedto send an alert to the user's mobile device, even when the two are notconnected wirelessly. In some embodiments the system is adapted toprovide alerts (such as on the wearable device) in the case of eventsthat affect measurement, such as when the device is accidentallycovered. In some embodiments the system is adapted to predict the safeamount of time remaining to be spent in current conditions before asafety threshold is exceeded. These algorithms can take into account notonly the current UV conditions, but also forecast UV conditions ahead todetermine the safe time accurately. The predictions may take place onthe mobile device or in some alternatives on the wearable device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary system including a wearable UV sensingdevice and a mobile device.

FIG. 2 is an exploded view of an exemplary wearable device.

FIG. 3 shows the response of two commercially available UVI diodes andsensors in comparison to the erythema action spectrum.

An exemplary algorithm for determining the environment based on sensorreadings is shown in FIG. 4.

FIG. 5 is an exemplary method of selecting the appropriate model forpredicting the erythemally-weighted UV exposure from the sensor values.

FIG. 6 shows the ratio of erythemally-weighted UVB toerythemally-weighted UVA as seen over the course of a day (every hour).

FIG. 7 shows the variation of R_(B/A) with the solar zenith angle.

FIG. 8 shows an exemplary method for the estimation of UVA and UVB.

FIGS. 9A and 9B illustrate an exemplary magnetic attachment system.

FIG. 10 illustrates an exemplary magnetic attachment system.

FIGS. 11A and 11B illustrate an exemplary charging system.

FIGS. 12A and 12B illustrate an angle the tilt (φ).

FIG. 13 illustrates an exemplary method of user notification.

FIGS. 14(a)(i) and 14(a)(ii) illustrate light with and without adiffuser.

FIG. 14(b) illustrates the angle between a normal and the incoming rayof light.

FIG. 15 illustrates an exemplary wearable device, including a diffusertherein and above a plurality of sensors also within the wearabledevice.

FIGS. 16A and 16B illustrate an exemplary proximity sensor, including alight source and a detector, and a covering material over the proximitysensor.

FIG. 17 illustrates an exemplary method for proximity detection using aproximity sensor.

FIG. 18 illustrates an exemplary method that can cause a device toswitch between a sleep mode and an active mode.

FIGS. 19A and 19B illustrate exemplary displays and a method of allowingusers to select a UV threshold based on a time history of symptoms andUV exposure.

FIG. 20 illustrates an exemplary embodiment of a method for setting athreshold.

FIG. 21 shows the variation of UV index over a typical day.

An exemplary computer executable method for estimating the safe amountof time to spend in current UV conditions is shown in FIG. 22.

DETAILED DESCRIPTION

The disclosure relates generally to methods, systems, and devices for UVsensing and estimation.

FIG. 1 is a block diagram of an exemplary system that can be adapted foraccurate measurement and real-time feedback of ultraviolet exposure, andcan incorporate any of the methods herein. The system in FIG. 1 includestwo sub-systems. The first subsystem is wearable device (100). Wearabledevice 100 includes a plurality of light sensors—a UV Index (“UVI”)diode (110), a UVA diode (UVA) (115), a visible light diode (VIS) (120),an infra-red LED (125) coupled with an infra-red detector (PROX) (130).Additionally, the wearable device also includes one or more orientationsensors (ORIENT) (135) capable of determining the orientation of thewearable device in space. Sensors 110, 115, and 120 are in communicationwith a microcontroller (150) via one or more transimpedance amplifiersA1-A3, respectively (111), which itself is powered by an on-boardbattery (140). The battery is capable of being recharged via a charger(145). Microcontroller 150 transmits collected data via a wirelesstransmitter (155) following a certain protocol such as Bluetooth LowEnergy, which is known.

The exemplary system in FIG. 1 includes a second subsystem—mobile device160. The mobile device may also be referred to as a “remote” device.Mobile device (160) can be a typical handheld device such as asmartphone or tablet, which has a wireless receiver (165) that followsthe same protocol as the transmitter on the wearable, e.g., BluetoothLow Energy. Collected data is received by an application (170)executable on mobile device (160), which interfaces with the user via adisplay (175) that includes one or more pieces of information about theuser's UV exposure. This display can be the screen of the mobile device.

An exploded view of an exemplary implementation of wearable device 100is shown in FIG. 2. The wearable device includes a housing comprisingtop case 101 and bottom case 105, which contain therein internalcomponents. Top case (101) is made of opaque material and has aplurality of windows 106 therein that allow light to reach the sensorsthat are disposed on a printed circuit board (PCB) (103) within thehousing. In this exemplary embodiment, the device includes UVI sensor107 disposed below the central window, proximity and visible lightsensor 108 disposed below a peripheral window, UVA sensor 109 disposedbelow a second peripheral window, and a LED that cannot be seen in FIG.2 because it is obscured by diffuser 107, but is disposed on printedcircuit board 103 below a third peripheral window (the top window in thefigure). In this exemplary embodiment the top case 101 includes a UVIsensor window, a UVA sensor window, a window for a sensor that includesboth a proximity sensor and visible light sensor, and a LED lightwindow, but in other embodiments it can have a different number ofwindows depending on how many objects disposed in the housing need toreceive light, and their relative positions. Diffuser 102 is disposedbetween the top case 101 and the PCB 103, which is adapted to capturelight from different angles and project them on to the sensors below.The PCB 103 rests on a magnet (104), which is optionally annular, whichengages and attaches to the bottom case (105). The bottom case and thetop case are secured to one another. The magnet can be is used in anattachment system, examples of which are described herein, wherein anexternal magnet allows the wearable device to be clipped on to anyarticle of clothing. Microprocessor 110 is also shown on PCB 103.

The exemplary system has a unique combination of sensors: a UVI sensor,a UVA sensor, a visible light sensor, a proximity sensor, and anorientation sensor, as well as unique algorithms that can utilizeinformation from one or more of the sensors. The following sub-sectionsdescribe how the sensors and algorithms can all work, some individuallyand some together, to improve either the accuracy of measurement orreal-time feedback of ultraviolet exposure. Not all of the algorithmsdescribed herein need to be performed with each other. In fact, any ofthe algorithms herein can be used individually.

The UVI, UVA and visible light sensors are all light sensors, but theyhave different responses to light. The optional UVA diode, examples ofwhich are known, has a peak of measurement in the UVA region (315-400nm) and has very low response outside this band. Similarly, the visiblelight diode, examples of which are known, has a peak of response in thevisible light region (400-800 nm), and near-zero response outside thisband. The UV Index (UVI) diode has a unique response that attempts tomatch the erythema action spectrum (see McKinlay, A. & Diffey, B. “Areference action spectrum for ultra-violet induced erythema in humanskin”. CIE J. 17-22 (1987)) by weighting the UVB (280-315 nm)exponentially higher than the UVA (315-400 nm), to mimic the impact ofUV on the human body. This measurement is called erythemally-weightedUV. FIG. 3 shows the response of two commercially available UVI diodesand sensors in comparison to the erythema action spectrum.

In alternative embodiments, however, not all of the UVI, UVA, proximity,visible, and orientations sensors are included in the wearable device.For example, a UVA sensor is optional if information from a UVA is notneeded for a particular method. Similarly, a visible light sensor isoptional if an algorithm need not receive information from a visiblelight sensor. In some embodiments the device does not include anorientation sensor if the orientation is not needed or desired.

A previous experiment (E. Thieden et al., “The wrist is a reliable bodysite for personal dosimetry of ultraviolet radiation”, Journal ofPhotodermatology, photoimmunology & photomedicine, Vol. 16, Issue 2,2000) has observed that there is poor correlation between measurementsof UV exposure on different parts of the human body (e.g., measuring onthe wrist correlates poorly with measuring on the top of the head).Since a primary goal of the disclosure herein is accuracy of UV indexestimation, the systems herein generally measure UV exposure on aspecific part of the body only. For UV-sensitive patients, long-sleevedclothing and long pants cover most of the body from UV exposure, but theface is usually left exposed (since no one wears a mask in broaddaylight). Therefore, in some embodiments, the system is adapted toaccurately measure UV radiation dose incident on the face. The followingsub-sections will list several characteristics of exemplary systems thatcan enable this.

1. Real-Time Correction Using Environment Detection

Measurement of erythemally-weighted UV (UV Index) from the solarspectrum is very prone to error. One of the primary factors affectingthe accuracy of measurement is the environment in which the device isbeing used. Broadly speaking, there are two usage environments—indoors(220) and outdoors (250). Indoors can be further subdivided as being indirect sunlight 230 (through windows), or away from sunlight 235.Outdoor environment can be characterized as being in the open or in theshade 290. The open can be separated into sunny 280 or cloudy 270. Sincethe sensors are usually calibrated for only one type of environment,they will be erroneous when used in other types of environments. It isthus important to identify the environment and correct the output of thesensors accordingly, depending on the environment.

This exemplary system identifies the following environments:

(a) Indoors (220), in direct sunlight through windows (230)

(b) Indoors (220), away from direct sunlight (235)

(c) Outdoors (250), in shade (290)

(d) Outdoors (250), in the open with sunny weather (280)

(e) Outdoors (250), in the open with cloudy weather (270)

An exemplary algorithm for determining the environment based on sensorreadings is shown in FIG. 4. This is a decision tree algorithm based onthe readings from the UVI, UVA and visible light sensors (200). The nextsection will describe how these sensors are used to separately estimateerythemally-weighted UVA and UVB, but for this section it is assumedthat the values have already been derived. We know that UVB is absorbedby glass and hence drops to undetectable levels when indoors. The sameis not true for UVA, which is usually transmitted through glass. Thus,at the first level of the decision tree, we utilize the UVB value incomparison to a threshold UVB_(th) to determine if the user is indoorsor outdoors (210). The value of the threshold is trained a priori bycollecting data from several users in both indoor and outdoorsituations. A maximal margin separating hyperplane method (e.g., Cortes,C.; Vapnik, V. (1995). “Support-vector networks”. Machine Learning 20(3): 273. doi: 10.1007/BF00994018) can be used to train this thresholdfrom the collected data.

If the user is determined to be indoors, the algorithm then utilizes theUVA sensor value to decide if the user is in direct sunlight through thewindows or away from it. The algorithm then compares this UVA sensorreading to a threshold UVA_(th,indoor), (225) which can be set using thesame set of machine learning methods described above. It is known thatUVA partially travels through windows, which makes the UVA value higherwhen in sunlight through the windows, and lower when away from thewindow.

If the algorithm determines the user is outdoors, the algorithm utilizesthe reading of the visible light sensor (VIS) to determine if the useris in shade or in the open. The algorithm then compares the reading fromthe VIS sensor to a threshold VIS_(th,shade) (255). Being lower than thethreshold implies shade, while being above the threshold indicates beingin the open. This threshold can be trained using data collected from anumber of users in both situations. Finally, if in the open, the sensorvalues can further be utilized to determine whether the weather iscloudy or sunny. This is achieved using both the visible light readings(VIS) and the UVB reading (260). We know that clouds attenuate thevisible light, but transmit UVB, while in sunny weather both VIS and UVBare high. We formulate this determination of cloudy vs. sunny as anoptimization problem, where:

$\begin{matrix}{{{Environment} = {Cloudy}},{{{{if}\mspace{14mu} a_{1}U\; V\; B} + {a_{2}V\; I\; S} + a_{3}} < 0}} \\{{= {Sunny}},{{{{if}\mspace{14mu} a_{1}U\; V\; B} + {a_{2}V\; I\; S} + a_{3}} \geq 0}}\end{matrix}$

The parameters a₁, a₂ and a₃ can be trained using data collected withthe devices placed in sunny and cloudy conditions. A maximal marginseparating hyperplane algorithm (also known as a support vector machine)can be used to determine the optimal value of these coefficients. Theabove sunny vs. cloudy determination has been described as a two-classproblem, but it can also be described as a multi-class problem to detectdifferent cloud densities e.g., scattered light clouds vs. overcast.Solving such a multi-class problem would involve training severalone-vs-all classifiers—one for each class that we are interested in.

Once the environment is detected, the device is able to select theappropriate model for predicting the erythemally-weighted UV exposurefrom the sensor values—FIG. 5. We refer to it as the UV Index, althoughstrictly speaking the UV Index is for horizontal measurements and thedevice presented here has an orientation similar to the user's face. TheUV Index is modeled as a polynomial function of the UVI, UVA and VISsensor values (s_(uvi), s_(uva), s_(vis)):

UVIndex=f(s _(uvi) ,s _(uva) ,s _(vis))

The form of the polynomial function is derived during the calibrationprocess. If we fit only one calibration function or model (f) for allenvironmental conditions, it suffers from a lack of accuracy. Forexample, a model that is calibrated on data collected across a varietyof environments will not be particularly accurate for just the indoorenvironment. However, using multiple models, each of which is calibratedto data from a particular environment allows each model to be moreaccurate for only its particular environment. This exemplary embodimentuses five such models, corresponding to our five environments describedabove, which is stored in a calibration database (320). When theenvironment is detected (310) using our aforementioned decision treealgorithm, the system is able to select the most appropriate calibrationfunction (350), which is then used with the sensor values (300) toderive the UV Index (330). This gives the most accurate measurement ofthe UV Index in all possible environments. The UV Index can then be, forexample, displayed to a user on a display.

2. Separation of UV Measurement into UVA and UVB

The importance of separating UV dose measurement into UVA (320-400 nmwavelength) and UVB (280-320 nm wavelength) has already been elucidated.UVA has very different impact on the human body as compared to UVB.Different amounts of UVA and UVB are required for activation of anadverse response, with the amount of UVB being much smaller than UVA forthe same adverse response. To weigh the consequences of UVB and UVA onan equal footing, it suffices to compare erythemally-weighted UVB andUVA. Here we describe two exemplary methods to measure erythemallyweighted UVA and UVB dose—one utilizing two UVI diodes with differentfilters, the other utilizing software-based estimation with a single UVIdiode.

In the first method, two diodes with identical response similar to theerythema spectrum are placed in the wearable device, one underneath afilter that lets pass the UVA region of the spectrum and nothing else,the other one underneath a similar filter for UVB. Since perfect filtersfor the said regions of the spectrum do not exist in practice, thismethod introduces errors, the first consequence of which is that theaddition of the responses of both diodes (even when normalized to thepeak transmission of each individual filter) may not be equal to thefull erythema spectrum, hence the UVI cannot be retrieved from thisdevice, even if the response curve of the original diodes were to matchperfectly the erythema curve.

Another embodiment of the above concept makes use of diodes withdifferent responses each, and also different filters. The combination ofeach diode response and filter tries to match as closely as possible theUVA portion of the erythema spectrum in one case, and the UVB in theother.

In either case, this configuration utilizing two diodes resembles thatof the UVA and UVI diodes in FIG. 1, in that each is connected to ananalog amplifier, then analog to digital converter and then the responseis read in the microcontroller.

The above method has the drawback of utilizing two diodes, which makesit take up more area and increases expenses. We propose an alternativescheme for separating UVA and UVB dose estimation using a single UVIdiode, coupled with a mobile device which has knowledge of the currentlocation and local time. FIG. 6 shows the ratio of erythemally-weightedUVB to erythemally-weighted UVA as seen over the course of a day (everyhour). Erythemal weighting gives exponentially higher weight to UVB asopposed to UVA, but the solar spectrum also contains much higherquantities of UVA as compared to UVB. The plot shown is for a locationin France in summer. This ratio varies with location (latitude inparticular), as well as time of the year. There are lower amounts of UVBduring winter, and higher amounts during summer.

The erythemally weighted UVB/UVA ratio (R_(B/A)) is modeled as afunction of solar zenith angle (φ). FIG. 7 shows the variation ofR_(B/A) with the solar zenith angle. We fit a sinusoidal function tothis data, which allows us to model the UVB/UVA ratio as a function ofthe solar zenith angle.

R _(B/A) =p ₀ +p ₁ sin φ  (Eq. 2.1)

The flow for estimation of UVA and UVB using this method is shown inFIG. 8. The mobile device, such as mobile device 160, has informationabout the current location and time of the measurement (400). This isused to look up the solar zenith angle for an existing database (410).The solar zenith angle (SZA) is readily available via internet APIs orcan be computed using well-known models. With knowledge of the SZA (φ)(420), and the coefficients p₀, p₁ (430), we calculate the UVB/UVA ratiousing Eq. 2.1 (440). The system then estimates in real time, the amountof erythemally-weighted UVB (EUVB) and erythemally-weighted UVA (EUVA)separately (460, 465) from the UV Index (450) using the followingequations:

$\begin{matrix}{{E\; U\; V\; B} = {25\frac{mW}{{cm}^{2}}U\; V\; {Index}\frac{R_{B/A}}{1 + R_{B/A}}}} & \left( {{Eq}.\mspace{11mu} 2.2} \right) \\{{E\; U\; V\; A} = {25\frac{mW}{{cm}^{2}}U\; V\; {Index}\frac{1}{1 + R_{B/A}}}} & \left( {{Eq}.\mspace{11mu} 2.3} \right)\end{matrix}$

The factor of 25 accounts for the fact that one unit of UV Indexcorresponds to 25 mW/cm² of erythemally weighted ultraviolet radiance(McKinlay, A. & Diffey, B. “A reference action spectrum for ultra-violetinduced erythema in human skin”. CIE J. 17-22 (1987)). The UVA and UVBestimate can then be used in any methods herein, such as estimating theUV index.

3. Magnetic Attachment Method

Ultraviolet exposure on one region of the body often does not correlatewith other regions. For example, E. Thieden et al., “The wrist is areliable body site for personal dosimetry of ultraviolet radiation”,Journal of Photodermatology, photoimmunology & photomedicine, Vol. 16,Issue 2, 2000, found that exposure on the chest does not correlate wellwith the top of the head, so measuring one does not give a clear idea ofthe other. The systems herein are generally configured and adapted tomeasure ultraviolet dose on the face. We observe that other portions ofthe body can be adequately shielded with clothing options such aslong-sleeved shirts, trousers and shoes, but the hands and the face arethe most difficult to shield due to lack of sufficient clothing options(we don't expect people to wear masks or gloves on a summer dayoutdoors). While the hands are continually in motion and will receivevariable amounts of UV dose, the face is relatively stable. This is whymeasuring UV exposure on the face has advantages. For this purpose, insome embodiments the system includes a magnetic wearable system that iscapable of being attached to the front of the top layer of clothing,usually a shirt. This sensor is generally always oriented in the samedirection of the face, and hence will collect a UV exposure dose thatcorrelates very closely with that of the face. Measuring on the chestalso provides the advantage of having a very stable measurement, asopposed to the wrist.

The magnetic attachment system shown in FIGS. 9(a) and 9(b) comprisestwo magnets, one (710) disposed inside the wearable device housing andone (712) on the outside of the wearable device housing (700). Themagnet in the inside of the wearable device (710) housing sits close tothe bottom of the unit (740), and the wearable device is meant to beplaced on top of the outer layer of clothing (750) in the upper torsoregion of the user (see FIG. 9(b). The other magnet is meant to beplaced on the opposite side of the outer layer of clothes. In thismanner, the attraction of the 2 magnets makes the device press againstthe fabric of the garment, providing a secure grasp.

Whereas the user can freely choose any place in the fabric of thegarment to place the device, its intended area of use is in the uppertorso (770), as depicted in FIG. 9(b). This method is superior to othersbased on specific features in clothing, such as clips, which can only beplaced on edges of clothing. It is also superior to pin or broochattachments in that it does not pierce the clothing. It is conceivablehowever, that in some embodiments there the wearable device can bepositioned elsewhere.

This system includes similarly shaped (e.g., cylinders of same diameter,rings of same internal and external diameters, but not necessarilyheight) magnets (see FIG. 10), as projected to the plane that lies inbetween them in order to ensure that they are aligned when snappedtogether. The ring-shaped magnets allow for the design of a particularcharging system, as described below.

4. Charging System

An exemplary charging system shown in the side and perspective views ofFIGS. 11A and 11B uses conductive, concentric ring shaped conductors(810) in the bottom of the device (800), which are connected todifferent signals in the internal circuitry of the device. The chargermakes use of spring loaded contacts (820) in a flat configuration, atvarying distances from a common axis of symmetry normal to the saidplane, which coincide with the radii of the conductive rings on thedevice, and carry the electrical signal intended to make connection withthat specific ring. This is depicted in FIGS. 11A and 11B. In this way,electrical connection is ensured, irrespective of the relative rotationangle between the device and the charger around the common axis ofsymmetry.

The charger may optionally also include a magnet or ferromagneticmaterial. This will cause magnetic attraction to the magnet inside thedevice housing and allow for better engagement of the charger anddevice. The strength and position of such a magnet is also adjusted sothat the magnetic clamping causes the electrical contacts on both deviceand charger to align correctly with each other.

5. Sensor Value Correction Using Orientation Detection

As described above, the wearable device (100) can be attached to thefront of the clothing using a magnetic attachment system. The purpose ofthe wearable device is to measure the exposure on the face (I_(face))(510), and hence needs to be aligned as flat against the chest aspossible. However, depending on the material of clothing used and wherethe device is placed, the device may, in practice, be tilted from thisideal flat position corresponding to the face orientation (520).Further, the tilt of this device might be changing very rapidly, such aswhen the wearable is attached to a loose shirt while the user isrunning. This would cause an unstable measurement, despite the user'sface receiving a uniform amount of UV exposure. Stability and accuracyare both important, in order to accurately estimate UV dose. We usesensors to detect the device orientation (530) in real-time. Thisknowledge is then used to correct the measured exposure (I_(device))(500) to correlate to that on the face. This serves the dual purpose ofcorrecting errors and stabilizing the measurement of UV.

Orientation detection is performed by a set of orientation sensors(e.g., orientation sensor 135, in FIG. 1) including accelerometers andgyroscopes, which are known. These determine the angular position of anobject in three dimensions in terms of pitch, roll and yaw. We areprimarily interested in the angular rotation of the device around thehorizontal axis passing from left to right through the human face. Wewill call this angle the tilt (φ) (FIGS. 12A and 12B) (540). The tiltangle is an output from the orientation sensor, or derived from outputfrom the orientation sensor, and is input to computer executable methodsherein.

The actual irradiance incident normally on the face (I_(face)) can bethen estimated by the system in terms of the tilt and the irradianceincident on the device (I_(device)) as:

I _(face) =I _(device) COSφ

6. Real-Time Notification from Wearable Device to Mobile Device UsingGeo-Fencing

The wearable device (100) can be adapted to able to alert the user incertain scenarios e.g. when the daily UV exposure has exceeded safelimits, or the wearable device is running out of battery, or thewearable device is being obstructed by something. We will broadly referto such a situation as an alert condition. The notification needs tohappen soon after the alert condition is detected on the wearabledevice, so as to not risk the user's health, and hence needs to be inreal-time. We cannot assume that the wearable device is always connectedto the user's mobile device wirelessly. This is due to a number ofpractical reasons e.g., the user might have dismissed the mobileapplication on their mobile device, or the OS of the mobile device mighthave severed the wireless connection in order to conserve battery.Further, in most wireless protocols, the slave cannot initiate contactwith the master. In this case, the slave is the wearable device, themaster is the mobile device, and this is a common condition forBluetooth/Bluetooth Low Energy. Under such circumstances, we propose anovel and unique method to notify the user of the alert condition, basedon geo-fencing.

Geo-fencing is the science of alerting a mobile user when the device hasentered a particular location. Normally, this location is determinedusing the GPS chip on the mobile device, although increasingly commonlyWiFi signals are also being used to improve this location estimate.Beacon-based geo-fencing allows even more fine-grained locationestimates by being able to determine if the mobile device is in thevicinity of a Bluetooth beacon whose location is known a priori.Previously, this has purely been used for more accurate locationestimates, but our proposed system utilizes the same method for sendingalerts from any Bluetooth-enabled device.

FIG. 13 shows an exemplary flow for user notification. The applicationon the mobile device (670) can be set up for beacon-based geo-fencing(675). This allows the device to be alerted whenever it is in thevicinity of a beacon with a specific identifier. This alert identifieris known to both the wearable device and the mobile device and stored ina database (660), which may exist in-memory on the wearable device andmobile device, or reside in the cloud. Three alert conditions may existon the device: (a) the wearable device is covered by an object e.g. theuser's jacket (610) (b) the measured UV dose exceeds the user's selectedthreshold (620), or (c) the wearable device is running low on battery(630). When the microcontroller on the wearable device (640) detects itsalert condition, it switches to advertising with that same pre-specifiedalert identifier (650), which it looks up from the database (645). Theidentification information is contained in the advertisement packet ofthe beacon (655). The system utilizes different identifiers to indicatedifferent alert conditions. When the mobile device is alerted of thepresence of a beacon (680), it first derives the alert identifier fromthe beacon advertisement packet (681). It then checks its identifieragainst its list of known identifiers (682). If the identifiercorresponds to a known alert condition, the mobile device displays thisalert condition to the user (685). If the user acknowledges the alertcondition, the mobile device then connects wirelessly (note that themobile device as the master can initiate connection) and sends anacknowledgement to the wearable device (690). This acknowledgementcauses the wearable to stop advertising as a beacon (691) and resumenormal operation by clearing the alert condition (692).

7. Use of Diffuser with Cosine Response

In some embodiments the wearable device is adapted and configured suchthat the sensors lie under an opaque casing. In order for light to reachthese sensors, the casing can include windows in the material totransmit light. However, depending on the angle of the incident lightand the depth under the casing where the sensor lies, it is easilypossible for incident light to not reach the sensor, thus givinginaccurate readings (FIG. 14(a)(i)). For this purpose, the casing shouldhave a material that is capable of accepting light at different incidentangles and removing this angular information when transmitting it to thesensor below (FIG. 14(a)(ii)). In some embodiments the wearable devicethus includes one or more optical diffusers as the filling material forthe aforementioned windows. Here we describe the desired response of thediffuser material.

The amount of irradiance in a flat area element A from a planar sourceof light (direct light from the sun can be assumed to be a planarsource, since the origin of the rays is so far away that they are almostparallel) reaches a maximum when the normal of the element is parallelto the incoming rays. Let's call this maximum I_(max). If the area isthen tilted so that the angle between its normal and the incoming raysis θ (as seen in FIG. 14(b)), then the irradiance varies as a cosine ofθ multiplied by the maximum radiation. Note that this is independent ofrotation of the said area element around its normal.

Irradiance of a tilted plane can be expressed then as a function of θsuch that:

I(θ)=I _(max) cos(θ)  (Eq. 7.1)

In order to be true to the physical quantity being measured, thewearable device should exhibit the same angular response when the sensoris tilted with respect to the sun. The optical diffuser, placed on topof the UV and optical sensors, needs to have the properties of a perfectLambertian diffuser, which will allow the recovery of the desired cosineangular response (Eq. 7.1). The device includes windows of a specificmaterial aimed at resembling as close as possible a Lambertiantransmission diffuser. The diffuser material may be cut intowindow-shaped pieces and adhered underneath the openings to allow thelight in, or may be assembled as a single piece directly underneath thewindows using clips in the casing, as depicted in FIG. 15. In thisdepiction, the top case (1050) comprises clips (1030) into which thesingle-piece diffuser (1040) is able to snap in place, and be heldfirmly. The plurality of windows in the top case are directly positionedabove the sensors of interest (1010, 1020), which reside on the printedcircuit board (PCB) (1000).

8. Covering Detection and Alert

As previously described, in some embodiments the wearable device ismagnetically attached to the front of the clothing. It is possible thatthe user mistakenly covers this device, such as when wearing a jacketover the shirt. This would cause the covering to block all UV to thedevice, and thus render it unable to estimate the radiation incident onthe face. In order to overcome this problem, in some embodiments thewearable device includes a covering detection system, which is capableof alerting the user, so that the covering may be promptly removed.

In this embodiment, in order to detect covering, a proximity sensor(e.g., proximity sensor 130 in FIG. 1) is used, which includes aninfra-red (IR) LED (1100) and an IR detector (1110). The IR LED sendspulses outward (1130). The two components are place under a window ofthe top case (1150), which is covered by diffuser material (1120).Without any covering items, the IR pulses escape and are not captured bythe IR detector (see FIG. 16A). If any object is covering the wearable(1140), there is significantly high reflection of IR from it and ispicked up as a signal in the IR detector, as shown in FIG. 16B.

The flow for proximity detection is shown in FIG. 17. Themicro-controller (1170) pulses the IR LED (1171) and polls the value ofthe IR detector (1172) in sequence. If the IR detector signal (PROX) isfound to exceed a certain proximity threshold (PROX_(th)) (1174), thenthe microcontroller increments a counter (1176), else clears the counter(1178). When the counter (Counter_(PROX)) exceeds a pre-specifiedthreshold (1180), the microcontroller determines that there is materialcovering the wearable device. It then triggers an alert condition(1182), which in turn will notify the user that their device is coveredby something.

9. Night Detection for Sleep Mode

The wearable device needs to not only be accurate, but alsopower-efficient so that it is able to maximize the amount of UV datacaptured on a single charge. For this purpose, collecting UV data in theabsence of the sun i.e. before dawn or after dusk, is an unnecessarydrain on the power supply. Being able to sleep during this time savesboth battery and memory for collecting data. However, it is not expectedthat the wearable device will be constantly connected to the mobiledevice, which would make it unaware of sunrise and sunset times. Inorder to overcome this issue, we utilize an algorithm based on theexisting sensors, which determines when to sleep and when to wake up thedevice.

FIG. 18 shows an exemplary sleep mode algorithm in more detail. In thedesigned system, there are two modes—sleep mode (900) and active mode(910). In active mode all sensors are active and the microcontrollerpolls these sensors to aggregate the UV data. From polling the visiblelight sensor (950) it determines if the reading (VIS) is above a certainthreshold. It also polls the proximity sensor (PROX) to ensure thatthere is nothing covering the device. If the reading is found to bebelow a pre-determined light/dark threshold (VIS_(light/dark)) (940),and the proximity reading exceeds the covered threshold (945), a counteris incremented (930), else the counter is cleared (935). If the counterexceeds a pre-specified value (Counts_(dark)) (920), indicating thecondition of darkness has persisted for some time, the device is putinto sleep mode (900). Running a counter-based scheme helps preventagainst noisy readings, or sudden darkness conditions e.g., when a trainpasses through a tunnel. If the proximity sensor senses something iscovering the device rather than darkness due to the absence of sun, thesystem can send an alert to the user, as described above.

In sleep mode all sensors apart from the visible light sensor are shutdown. The visible light sensor is also polled (950) at a much reducedinterval by the micro-controller in order to conserve more energy. Ifthe visible light reading is found to cross the same light/darkthreshold (VIS_(light/dark)) (940), then the microcontroller puts thedevice back into active mode.

10. User-Selectable Safe Thresholds Based on UV Exposure History

In order to avoid harmful effects of UV over-exposure (exposure over aprolonged period of time) such as sunburn or phototoxicity, it isimportant to understand and determine safe thresholds for UV dose(Sayre, R. & Desrochers, D. “Skin type, minimal erythema dose (MED), andsunlight acclimatization”. Am. Acad. dermatology 439-443 (1981);Heckman, C. J. et al. “Minimal Erythema Dose (MED) testing”. J Vis. Exp.e50175 (2013). doi:10.3791/50175). We have already described a systemfor alerting the user when such safe thresholds are exceeded. Here wedescribe a method for selecting such a threshold based on past exposurehistory, along with disease activity. We define the term diseaseactivity to indicate symptom occurrences and general well-being of theuser, as tracked on a periodic basis via the mobile application.Symptoms include skin reactions (e.g., erythema, sunburn, etc.) andsystemic symptoms (e.g. joint pain, etc.). Our system asks the user torate their disease activity daily on a scale of 0 (no symptoms, goodhealth), to 10 (lots of symptoms, poor health). Note that the thresholdmay apply to a full day's UV dose, or to some other time unit, such as aweek, or an hour. The unit of time may also be user-selectable, e.g., auser may choose to select a threshold for hourly UV dose, and adifferent threshold for daily UV dose. We will describe the rest of thissection using daily threshold as an example, but it easily extends toother time periods. Also, we will describe the example using UV dose,but it is equally applicable to UVA dose or UVB dose individually. Bylooking at both disease activity and UV dose, the user decides to managea dose of UV exposure that he or she thinks may be safe for his or herown wellbeing. Different users have different tolerances to UV and ourmethod enables anybody to manage the right amount of UV dose.

The threshold selection occurs on the mobile device, where all or someof the following information can be presented to the user:

(i) Minimum daily UV dose (over period of usage of the device)

(ii) Maximum daily UV dose (over period of usage of the device)

(iii) Average daily UV dose

(iv) Symptoms by date

(v) UV dose history by date

FIGS. 19A and 19B show one depiction of this information. The top graphslabeled “UV daily exposure” represents UV dose in units of Joules/m² (B.L. Diffey et al., “The standard erythema dose: a new photobiologicalconcept”, Journal of Photodermatology, photoimmunology & photomedicine,Vol. 13, 1997). This is visually presented on top of another graph witha representation of disease activity information, and can either be onthe same graph, or on an adjacent (the information can be presented inmany different ways). The disease activity is, in this embodiment, shownas a score, which was recorded by the user on a daily basis. The dailyminimum, maximum and average dose can also be shown on the plot. Themaximum of the UV dose on the Y-axis is set according to the maximumdaily UV dose ever received by the user. By understanding the timehistory of the symptoms, the user is then able to select a dailythreshold using a slider (or some other form of input), which liesbetween zero and the maximum UV dose the user has ever been exposed to.The threshold can be selected so that future symptoms can be avoided orminimized. For example, if a relatively high UV dose is associated withcertain diseases symptoms, as indicated on the screen, a user can selecta threshold dose that is below the level of the dose that was associatedwith the disease symptoms. Such thresholds can also be determined forUVA and UVB separately. Such a threshold can be determined for hourly,daily, weekly, monthly doses. Threshold can be chosen over any number ofhours, days, weeks, months, and in some embodiments the user can selectthe time epoch for which to set this threshold. In some embodiments thetime histories are broken up into epochs of time, and can be the sameepochs, or they can be broken up into different epochs of time.

One embodiment of the user interaction flow for setting the threshold isshown in FIG. 20. The process is started with the user requesting to settheir UV threshold (1200). This action may be in the form of tapping abutton on the mobile application (1290) (e.g., FIG. 19A), or may useother forms of input such as voice. When the mobile application receivesthis request, it fetches the user's UV exposure history (1210) from theUV exposure history database (1215), and the user's current UV thresholdfrom its respective database (1245). The database may reside on themobile device running the application, or in the cloud, in which casethe data would be retrieved over the internet. Concurrently, the user'sdisease activity information is also retrieved (1220) from the diseaseactivity database (1225). These two pieces of data are used to draw twobar graphs to display the information simultaneously (1230). It isimportant to view both pieces of data at the same time, since a safethreshold may only be inferred from how UV dose affected diseaseactivity in the past. The line corresponding to the current UV thresholdis drawn across the UV dose graph (1240), which is shown in FIG. 19A viathe horizontal line in the top graph, and the user is a given a visualcue of which days they exceeded their threshold by coloring bars abovethe threshold differently (1250) (as can be seen in the differenthighlighted areas above the line in the top graph in FIG. 19A, for anexample). When the user moves the threshold by dragging the thresholdline up or down (see FIG. 19B), the threshold line is re-drawn at thenew threshold value (1245). If the user confirms their new threshold bytapping on a confirmation button (1295) (shown in FIG. 19B), this newthreshold is saved in the UV threshold database (1245). This is anexample of how a user can select a threshold, and also optionally changea threshold after it has already been set. This ability to control thethreshold based on symptoms personalizes the threshold for each patient,providing much better care for the patient.

11. Accurate Estimation of Safe Amount of Time to Spend in CurrentConditions

While the wearable device measures the aggregated UV dose, it isdifficult for users to have a notion of how fast they are approachingsafe limits of UV dose (which may be user-selected, as describedherein). Thus, it is important that the system provide an estimate ofhow much time can be safely spent outside current weather conditions.The mobile device can provide this information, after the current UVdose has been wirelessly obtained from the wearable device. This timeestimate needs to be accurate, because overestimating the time can haveserious health consequences for the user, while underestimating the timedeprives the user of valuable healthy UV.

We assume that the current UV dose (D_(current)) and current UV exposureI_(current)) have been obtained from the wearable device, and a safethreshold (D_(safe)) for the UV dose is known, or has been pre-set bythe user. Note that both the current and safe dose may be related purelyto UVA, or UVB, or the combination of the two. The time to reach thedose limit (T_(safe)) can be estimated by solving the followingequation:

D _(current)+∫_(t=0) ^(T) ^(safe) I(t)dt=D _(safe)  (Eq. 11.1)

I(t) represents the UV exposure as a function of time. For accurateprediction of T_(safe), we need to have an accurate estimate for this.

UV exposure varies with the solar zenith angle (U.S. Pat. No. 9,068,887)(φ), which in turn is a function of time (t) as well as the location.FIG. 21 shows the variation of UV index over a typical day. We fit asinusoidal function to approximate this curve, which is also shown inthe figure. This allows us to approximate the UV exposure as:

$\begin{matrix}\begin{matrix}{{{I(t)} = {I_{\max}\sin \frac{\pi \left( {t - T_{sunrise}} \right)}{\left( {T_{sunset} - T_{sunrise}} \right)}}},{{{if}\mspace{14mu} T_{sunrise}} < t < T_{sunset}}} \\{{= 0},{{otherwise}.}}\end{matrix} & \left( {{Eq}.\mspace{11mu} 11.2} \right)\end{matrix}$

where T_(sunrise) and T_(sunset) represent the times of sunrise andsunset respectively. The information for these times is readilyavailable for a given location from internet APIs. The mobile device hasaccess to both such internet APIs and the location of the device. Themaximum UV exposure is estimated from the current UV exposure(I_(current)) by solving for the above equation at the current time(t_(current)).

$\begin{matrix}{I_{\max} = \frac{I_{current}}{\sin \frac{\pi \left( {t - T_{sunrise}} \right)}{\left( {T_{sunset} - T_{sunrise}} \right)}}} & \left( {{Eq}.\mspace{11mu} 11.3} \right)\end{matrix}$

By using this form of the function I(t) in Eq. 11.1, it is now possibleto analytically solve for the safe amount of time (T_(safe)) that can bespent in current conditions. This estimate can be updated continuouslyas new readings for UV exposure are received from the wearable device.In order to guard against sudden fluctuations in UV, e.g., when a cloudgoes over the sun, we also form an estimate for the current UV exposurebased on a weighted average of previous samples (Eq. 11.4).

I _(current)(t ₀)=a ₀ I _(current)(t ₀)+a ₁ I _(current)(t ₀ −T)+a ₂ I_(current)(t ₀−2T)+ . . . +a _(n) I _(current)(t ₀ −nT)  (Eq. 11.4)

Once this is calculated, this can be displayed on the mobile device tothe user, to inform them of the amount of time that is safe to be spentin the current environmental conditions. If the user is detected to beindoors (e.g., using any of the environmental detection algorithmsherein), then the time display can be dismissed and the mobile devicecan instead inform the user that they are safe from UV radiation.

An exemplary computer executable method for estimating the safe amountof time to spend in current UV conditions is shown in FIG. 22. Thewearable device sends the values of current exposure (1300) and currentdose (1310) using its wireless connection to the mobile device. Themobile device maintains a first-in-first-out (FIFO) queue (1320) tocache the past few values of UV exposure. From these values an averagecurrent exposure can be estimated (Eq. 11.4). The mobile device alsolooks up the user's pre-selected UV threshold from a database (1350)which might exist on the device or in the cloud. It also utilizes itsinternet connection to get sunrise and sunset times from a weather API(1360). With these pieces of information (1325, 1355, 1315, 1365), themobile device computes the safe amount of time for the user to spend incurrent conditions (1330), by numerically solving Eq. 11.1. Thisinformation is then displayed to the user (1340) using the mobiledevice's visual interface.

Any of the computer executable methods herein may be performed on awearable device (which in fact need not be worn, but could simply beplaced next to a subject, such as on desk) or on a mobile device, orsome parts of the computer executable methods may be performed on awearable device while some parts are performed on a mobile device. Thespecific examples herein are illustrative.

Additional concepts:

1. A wearable UV sensing device comprising a UVA sensor and a UVIsensor.

2. The device of concept 1 wherein at least one of the sensors comprisesa UV diode and a filter.

3. The device of concept 2 wherein the spectral response of the UV diodeand filter combine to mimic the erythemal weighting function.

4. The device of concept 1 wherein the sensors have the same response.

5. The device of concept 1 wherein the sensors have different responses.

6. A wearable UV sensing device comprising a UVA sensor, a UVI sensor,and a visible light sensor.

7. A wearable UV sensing device comprising:

a wearable sensing housing comprising a first magnetic element, and asecond magnetic element disposed outside the housing.

8. The device of concept 7, wherein the second magnetic element is notphysically attached to the housing.

9. The device of concept 7 wherein the second magnetic element isphysically attached to the housing.

10. The device of concept 7 wherein the first and second magneticelements have substantially the same shape.

11. The device of concept 10 wherein the first and second magneticelements do not have the same dimensions.

12. The device of concept 7 wherein the first magnetic housing isdisposed within the housing.

13. The device of concept 12 wherein the first magnetic element isdisposed in a plane that is parallel with a bottom surface of thehousing.

14. The device of concept 13 wherein the first magnetic element iscloser to the bottom surface than a top surface of the housing.

15. A charging system for a wearable UV sensing device comprising:

a wearable housing comprising a central conductor and at least oneannular conductor around the central conductor, the conductors disposedat an external surface of the housing;

a charger including at least first and second conductive contacts, thefirst and second contacts spaced from each other in the charger and thecentral conductor and annular conductor spaced from each other such thatthe first and second contacts are in contact with the central conductorand the annular conductor, respectively, when the housing and chargerare engaged.

16. The charging system of concept 15 wherein the charger furthercomprises a first magnetic element that is magnetically attracted to asecond magnetic element disposed within the wearable housing.

17. The charging system of concept 16 first and second magnetic elementsare positioned and configured such that their magnetic attractionfacilitates the alignment of the contacts and the conductors.

18. The charging system of concept 16 wherein the first and secondmagnetic elements are substantially the same size.

19. A personal UV sensing system, comprising

a wearable UV sensing device comprising an orientation sensor, and aremote device; and

a computer implemented method that estimates irradiance on a face of anindividual utilizing irradiance incident on the wearable UV sensingdevice and an angle of tilt of the wearable UV sensing device relativeto a horizontal plane passing through a human face.

20. A system including a wearable device adapted to send an alert to aremote device, comprising:

a wearable device adapted to, upon detection of an event, advertise as abeacon with an identifier associated with the event;

a remote device adapted to detect the beacon, compare the identifierassociated with the beacon with a set of known identifiers, and create auser alert to the occurrence of the event.

21. The system of concept 20 wherein the remote device is furtheradapted to, upon a user acknowledgement of the alert, establish awireless connection with the wearable device and communicate anacknowledgement to the wearable device.

22. The system of concept 21 wherein the wearable device is furtheradapted to, upon receipt of the acknowledgement, stop advertising as abeacon.

23. The system of concept 20 wherein the event is at least one of: a UVexposure has reached a threshold amount, the wearable device is low onpower, and a sensor in the wearable device is obstructed.

24. A wearable UV sensing device, comprising:

a housing with an aperture therein and an optical diffuser disposed inthe aperture.

25. The device of concept 24 further comprising a UV sensor securedwithin the housing and disposed below the optical diffuser.

26. The sensing device of concept 24 wherein the optical diffuser is aLambertian, or substantially Lambertian, optical diffuser.

27. A wearable UV sensing device comprising a UV sensor and a proximitysensor.

28. The device of concept 27 wherein the proximity sensor comprises alight source and a light detector.

29. The device of concept 28 wherein the light source comprises aninfra-red LED and the light detector comprises an infra-red detector.

30. The device of concept 28 wherein the sensing device furthercomprises a controller that is adapted to pulse the light source andpolls a value of the light detector in sequence.

31. The device of concept 30 wherein the controller is adapted tocompare the value polled with a threshold to determine if the proximitysensor is covered.

32. The device of concept 31 further comprising a remote device adaptedto create an alert that the proximity sensor is covered.

33. The device of concept 27 wherein the UV sensor includes one or moreof a UVA sensor, a UVI sensor, and UVB sensor.

34. A device of any of concept 27-33 wherein the device furthercomprises a visible light sensor.

35. A UV sensing system, comprising:

a remote device with a user interface, the user interface displaying atleast one aspect of UV exposure history, the user interface furtherincluding a user input selector adapted to allow a user to select a UVthreshold based on the at least one aspect of UV exposure history.

36. The system of concept 35 wherein the user interface is adapted toallow a user to select a UV threshold based on a threshold continuum.

37. The system of concept 35 wherein the at least one aspect of UVexposure history includes UV dose exposure.

38. The system of concept 35 wherein the user input selector is at leastone of a text field, a slider, a selectable menu.

39. The system of concept 35 wherein the at least one aspect of UVexposure history includes a minimum and maximum exposure, and the userinput selector allows the user to select a UV threshold between theminimum and maximum UV exposure.

40. The system of concept 35 wherein the user interface further displayspatient symptoms as they are related to at least aspect of the exposurehistory.

41. A personal UV sensing device, comprising

a sensor housing and at least one UV sensor inside the housing, and atleast one reflection reducing element adapted to reduce reflection oflight therefrom.

42. The device of concept 41 wherein the reflection reducing element ismade of a reflection reducing material.

43. The device of concept 41 wherein the reflection reducing element iscoated with a reflection reducing material.

44. The device of concept 41 wherein the reflection reducing element isdisposed within the housing such that it isolates the light path of theUV sensor.

45. The device of concept 41 wherein the reflection reducing element isdisposed within the housing between the UV sensor and adjacentcomponents.

46. The device of concept 41 wherein the reflection reducing element ispart of the housing.

47. The device of concept 41 wherein the reflection reducing element hasa non-linear configuration that contributes to its adaptation to reducereflection.

48. The device of concept 41 wherein the reflection reducing element hasa height greater than a width.

49. The device of concept 41 comprising first and second reflectionreducing elements, each one disposed on a side of the UV sensor.

50. A wearable UV sensing device with a sleep mode, comprising:

a UV sensor;

a visible light sensor;

a computer implemented method that is adapted to use a signal indicativeof an output of the visible light sensor to determine if a condition ofdarkness has persisted, and to initiate a sleep mode of the device.

51. The device of concept 50 wherein the computer implemented method isadapted to deactivate or reduce the use of the UV sensor in sleep mode.

52. The device of concept 50 wherein in the sleep mode the visible lightsensor remains activated to some extent.

53. The device of concept 50 wherein the computer implemented methodincludes a counter that is incremented when the signal indicative of anoutput of the visible light sensor is above a certain threshold, andwhen the counter reaches a threshold value, initiates the sleep mode.

54. The device of concept 50 wherein the computer implemented method isadapted to poll the visible light sensor in sleep mode and to determineif a condition of lightness has persisted, and if so, initiate an activemode of the device in which the UV sensor is activated.

55. The device of concept 50 wherein the computer implemented method isadapted to poll the visible light sensor in sleep mode at a reduced ratecompared with an active mode of the device.

56. A personal UV sensing system, comprising

a wearable sensing device and a remote device,

a computer implemented method that receives as input a signal that isindicative of an output from a UVI diode on the wearable sensing device,and compares the input to a threshold UV characteristic to make adetermination if the UVI diode is outdoor or indoors.

57. A personal UV sensing system, comprising

a wearable sensing device and a remote device,

a computer implemented method that receives as input a signal that isindicative of an output from a UVA diode on the wearable sensing device,and compares the input to a threshold UVA characteristic to make adetermination that the UVA diode is near a window indoors or away from awindow indoors.

58. A personal UV sensing system, comprising

a wearable sensing device and a remote device,

a computer implemented method that receives as input a signal that isindicative of an output from a visible light sensor on the wearablesensing device, and compares the input to a threshold visible lightcharacteristic to make a determination that the light sensor is in theshade or not in the shade.

59. A personal UV sensing system, comprising

a computer implemented method that receives as input a signal that isindicative of an output from a visible light sensor on the wearablesensing device and a signal that is indicative of an output from a UVIdiode on the wearable sensing device, and utilizes the signals to make adetermination if the visible light sensor and the UVI diode are in acloudy environment or in a sunny environment.

60. Any of the systems of concept 56-59, wherein the system is furtherconfigured to select a particular model for UV Index prediction based onthe determination made by the computer implemented method.

61. A personal UV sensing system, comprising

a wearable sensing device and a remote device; and

a computer implemented method that is adapted to use a signal that isindicative of an output from a UV sensor on the wearable sensing deviceand a solar zenith angle of the remote device to estimate amounts of UVAand UVB received by the UV sensor.

62. The system of concept 61 wherein the computer implemented method isadapted to calculate a quantitative relationship between UVB and UVAusing the solar zenith angle of the remote device.

63. The system of concept 61 wherein the computer implemented method isadapted to calculate a ratio of UVB to UVA using the solar zenith angleof the remote device.

64. The system of concept 63 wherein the computer implemented method isadapted to estimate the amounts of UVA and UVB using the signal that isindicative of an output from a UV sensor and the ratio of UVB to UVA.

65. The system of concept 61 wherein the computer implemented method isdisposed in the remote device.

66. A personal UV sensor system, comprising:

a wearable device and a remote device,

the system adapted to estimate an amount of time that can be spent inthe current weather conditions before reaching a threshold UV dose levelby forecasting a change in UV over time, the system further adapted todisplay the amount of time on the remote device.

What is claimed is:
 1. A computer executable method of increasing theaccuracy of UV monitoring, comprising: receiving UVB information that isindicative of an intensity of UVB light sensed by a UV sensor, the UVsensor disposed in a UV monitor; comparing the UVB information with athreshold UVB level to make a first determination if the UV monitor isindoors or outside; receiving secondary information indicative of lightoutside of the UVB range sensed by the UV sensor or a second sensordisposed in the UV monitor; using the secondary information to make asecond determination about the environment of the UV monitor; using thesecond determination about the environment to select one of a pluralityof environment models for predicting the UV Index; and predicting the UVIndex with the selected model.
 2. The method of claim 1, whereinreceiving secondary information comprises receiving secondaryinformation indicative of visible light sensed by a second sensor, thesecond sensor being a visible light sensor disposed in the UV monitor,and wherein using the secondary information comprises using thesecondary information to make a second determination about whether theUV monitor is outdoors and in the shade, or outdoors and in the open. 3.The method of claim 2 wherein making the second determination comprisescomparing the secondary information indicative of visible light to avisible light threshold.
 4. The method of claim 3 further comprising,using the UVB information that is indicative of an intensity of UVBlight sensed by a UV sensor and the secondary information indicative ofvisible light sensed by a second sensor to make a further determinationabout whether the UV monitor is in an open cloudy environment, or in anopen and sunny environment.
 5. The method of claim 4 wherein making thefurther determination comprises calculating if a polynomial is above anopen threshold, the polynomial comprising a first variable indicative ofthe UVB information, and a second variable indicative of the visiblelight sensed by the second sensor.
 6. The method of claim 1, whereinreceiving secondary information comprises receiving secondaryinformation indicative of an intensity of UVA light, and wherein usingthe secondary information comprises using the secondary information tomake a second determination about whether the UV monitor is indoors andin direct sunlight, or indoors and not in direct sunlight.
 7. The methodof claim 6 wherein using the secondary information to make a seconddetermination comprises comparing the secondary information indicativeof an intensity of UVA light to a UVA light threshold.
 8. The method ofclaim 1, wherein the computer executable method is stored in the UVmonitor.
 9. The method of claim 1, wherein the computer executablemethod is stored in a remote device, the UV monitor and the remotedevice adapted to communicate.
 10. The method of claim 1 furthercomprising presenting information on a remote device to the user, theinformation indicative of the predicted UV index.
 11. The method ofclaim 1 wherein receiving UVB information that is indicative of anintensity of UVB light sensed by a UV sensor comprising receiving UVBinformation that is indicative of an intensity of UVB light sensed by aUVI sensor.
 12. A computer executable method of estimating UVA and UVBwith a UVI sensor, comprising: receiving as input, from a remote device,a solar zenith angle; calculating a ratio comprising UVB and UVA usingthe solar zenith angle; receiving as input UVI information that isindicative of an output signal of a UVI sensor; calculating an estimatedUVB using the UVI information and the calculated ratio comprising UVBand UVA; and calculating an estimated UVA using the UVI information andthe calculated ratio comprising UVB and UVA.
 13. The method of claim 12wherein the ratio is a function of the solar zenith angle.
 14. Themethod of claim 12 wherein the estimated UVB is used in calculating atime history of UVB exposure of a subject, further comprising presentingthe time history of UVB on a display of the remote device.
 15. Acomputer executable method of modifying sensed UV signals based onorientation of a UV sensing device, comprising: receiving as input UVinformation indicative of UV light sensed by a UV sensor disposed in aUV sensing device; and estimating a UV irradiance incident normal to aface of a subject using an angle of tilt of the UV sensing devicerelative to a transverse plane of a subject, and the UV information, theangle of tilt derived from orientation sensor information from anorientation sensor disposed in the UV sensing device.
 16. The method ofclaim 15, wherein the UV information is indicative of UV light sensed bya UVI sensor.
 17. The method of claim 15 wherein the estimated UVirradiance is used in calculating a time history of UV exposure of asubject.